Electrooptical system and method of scanning



May 24, 1932- c. F. JENKINS 1,859,828

ELECTROOPTICAL SYSTEM AND METHOD OF SCANNING Filed Dec. 17, 1929 Tici.

C. FMA/Ad /s ./f/vmiv: INVENTOR ATTORNEY S Patented May 24, 1932 UNITEDSTATES PATENT OFFICE CHARLES FRAN GIS JENKINS, OF WASHINGTON, DISTRICTOF COLUMBIA, ASSIGi-NOR` TO JENKINS LABORATORIES, OF WASHINGTON,DISTRICT OF COLUMBIA, .A CORPORA- TION 0F THE DISTRICT 0F COLUMBIAELECTROOPTICAL SYSTEM AND METHOD 0F SCANNING Application led December17, 1929. Serial No. 414,627.

This invention relates lto electro-optical Vsystems and withparticularity to methods and means for scanning in television, picturetransmission and similar systems.

Heretofore various means have been devised for analyzing andsynthesizing an image, or other visual representation, employingrotating discs. For example, the N ipkow disc employs a series ofperforations arranged in the path of a single turn spiral. However, thistype of scanner is open to the objection that the scanning field islimited by the pitch of the spiral, and also the picture iield isradially distorted. v

In order to increase the size of the picture or scanning field it hasbeen proposed to employ a first disc having the perforations arranged ina plurality of convolutions, and another disc rotating in front of thefirst disc to act as a shutter in rendering each convolution of thefirst disc successively effective. This arrangement is open, however, toserious objections. The disc having the convolutions of perforationsmust be very large in order to provide a reasonably large picture field.Furthermore, the perforations in successive convolutions being atdifferent distances from the axis of rotation, the picture cannot bereproduced with uniform results since the edges of the picture willtaper toward the common center of the discs.

To overcome certain of the disadvantages of the latter system it hasbeen proposed to employ a drum having slots in the wall thereof, and aperforated shutter disc having a plurality of' convolutions ofperforations. This latter system likewise possesses seriousdisadvantages, which it is the purpose of the present invention toovercome. One of the main disadvantages is that the disc must rotate ina plane tangential to the drum periphery. Consequently the ydisc inmoving across the picture field produces a foreshortening `effect in thelight beam. Thus, considering the tangential point of relation betweenthe drum and disc, the disc perforations are of the same effective widthas the drum slots. However, as the drum rotates, because of thedivergent paths of the drum i wall and disc, the light is partially cutoff so that the effective cross section of the reproducing light beam isdifferent at the edges of the picture from the cross section at thecenter of the picture. Also, the disc must be mounted on a separateshaft, usually vat right angles to the drum shaft, requiring an eXpensive gearing and complicated driving arrangement.

Accordingly it isV one of the principal objects of the present inventionto provide a system of scanning wherein the above noted and otherdisadvantages are overcome. It is proposed to achieve this object byproviding two concentric scanning members in the form of circular drumsor cylinders one within the other and adapted to be driven at differentspeeds.

A feature of the invention resides in a twodrum scanner'. One drumhaving' a plu` rality of convolutions of scanning elements and the otherdrum having a slot or transparent helical strip acting as a shutter forthe first drum.

Other features and advantages not specifically enumerated will beapparent after a consideration of the following detailed descriptions,and the appended claims.

Referring to the drawings:

Figure l shows a sectional view of a scanning device embodying theinvention;

Fig. 2 is a view of one of the scanning drums of Fig. l;

Fig. 3 is a view of the other scanning drum of Fig l;

Fig. 4 is a plain schematic view showing the relation between the lighttranslating device and the scanning drums; and

Fig. 5 shows a modified form of scanning drum.

Referring more particularly to Fig. l, numeral l represents a suitablesupporting frame comprising the vertical standards 2 and 3, which areprovided with respectiveV bearings l and 5 for the main shaft 6. Shaft 6has attached thereto a pulley 7 adapted to 6, so that drum 9 rotates atthe same speed as shaft 6. The upright 2 is provided with a bearing 11through which passes the counter shaft 12. Shaft 12 at its left end isprovided with a spur gear 13 cooperating with gear 8, and at its righthand end carries a large' gear 14 cooperating with another spur gear'15attached to the hub of a drum 18 which is mounted for rotation aroundshaft 6, preferably in an anti-frictional manner as by ball bearings orthe like. The gear train 8, 13, 14 and 15 is so designed as to maintainproper ratio of angular speeds between the drums 9 and 18.

Referring to Fig. 2, it will be seen that the outer drum 18 is providedwith a series of scanning elements or preparations 19 ar-` ranged in thepath of a helix around the periphery of drum 18. The perforations 19 arepreferably spaced radially apart a distance corresponding to the widthof the picture iield to be scanned, as indicated by the letter Z Fig. 4.While Fig. 2 of the drawings show the perforations 19 arranged in fourcomplete convolutions around drum 18, it will be understood that anyother number of convolutions may be employed. The number of perforationsand the spacing therebetween, as well as the spacing between successiveconvolutions will, of course, depend upon the size of the drum and thenumber of linear elements along which the picture or image is to bescanned. F or example, if the picture field is to be scanned inforty-eight (48) successive A linear elements, then the perforations 19may be arranged in four (4) convolutions with twelve (12) perforationsin each convolution. Thus each convolution of perforations scans acorresponding strip of the picture field.` In order to prevent more thanone perforation 19 from being exposed in the picture field at al timethere is provided the drum 9, and for this purpose drum 9 is providedwith a continuous spiral light transmitting slot 20 which cooperateswith the successive perforations 19. In other words the drum 9 acts as ashutter for the drum 18 and successively renders each convolution ofperforations in drum 9 effective in scanning the picture field. Inasmuchas the entire picture field is scanned by a single revolution of drum 9while the picture field is scanned by four revolutions of drum 18, itwill be seen thatthe latter drum must be driven at four times the speedof the drum Y9. Because of the relative pitches of the convolutions indrum 19 and the slot 2O in drum 9, the picture field is eX- posed toonly one perforation 19 at a time, it being understood that the drum 9is driven in the same direction of rotation as the drum 18. For thepurpose of defining or limiting the width of the picture field asuitable aperture plate 21 is provided.

While the drums 9 and 18 may be made out of any suitable material, it ispreferred to make them out of light metal such as aluminum. However, inone embodiment Ythat was found to produce satisfactory results the outerdrum 18 was made of relatively thin aluminum while the inner drum 9 wasof glass having a non-transparent covering such as blackened paper orthe like around the periphery thereof, and with the spiral slot 20 cutout of the paper or covering, thus in effect producing the same resultsas a spiral slotted metal drum. This avoids the mechanical difliculty ofmachining a metal drum with a continuous spiral slot. Mounted withy inthe drums 9 and 18 in any suitable manner is a light translating lamp 22which may take the form of an inert gaseous lamp, preferably one of theneon filled type, and having a pair of electrodes 23 and 24, electrode24 serving as the luminous electrode and having dimensions preferablyslightly greater than the dimensions of the picture or image to bereproduced or scanned.

While any desired shape of perforation may be used in the drum 18, it ispreferred to employ one having a. circular or rectangular lightboundary. Furthermore the width of the slot 2O in drum 9 is preferablyslightly greater than the width of the perforations 19 in order to allowfor variations due to machining, wear, etc. When the device is to beused for reproduction the lamp 22 is connected to a source of currentshaving variations corresponding` to the elemental areas of the image orother visual representation that is being reproduced. Since the drums 9and 18 are rotating simultaneously before the stationary luminouselectrode 24, and since the said drums are rotating at different ratesof speeds in the same direction, and because of the diiferent pitches ofthe slot 20 and the convolutions of perforations in drum 18, an observerlooking at the drums through the opening in the aperture plate 21 seesthe image or representation reproduced in the form of a moving spot oflight in the manner well known in television reproduction.

As a result of this arrangement of scanning drums the image orrepresentation is reproduced with uniformity since the exposedperforations 19 are always at the same distance from the aXis ofrotation.

If it is desired to employ a metal shutter drum in place of the glassdrum 9 as shown in Fig. the drum may be formed with a spiral slot 25having integral bridge members 26 across the slot at suitable spacedintervals to provide the requisite rigidity to the drum. The strips 26may be made sufficiently narrow so that they do not interfere with thereproduction due to the high speed of rotation of the drums.

While the invention has been described hereinabove as appliedto ascanning mechanism for reproduction, it will be understood that it isequally well applicable for scanning to effect transmission in whichcase the device 22 will be replaced by a photo-electric cell and theimage or visual representation Will be projected upon the front of thedrums through the aperture plate 21 in any well known manner.

Vhile specific forms and arrangements of apparatus are disclosed herein,it will be understood that the invention is not limited thereto. F orexample while the drum 9 is shown as rotating within the drum 18, itwill be clear that drum 9 may be exterior to the drum 18. Other changesand modifications may be made without departing from the spirit andscope of the invention.

What is claimed is:

1. A shutter for television in the form of a hollow transparent drumhaving a non-transparent covering with a spiral light transmitting slotuin the peripheral surface thereof.

2. A shutter drum for television scanning,

comprising a glass drum having a non-transparent covering on theperiphery and a helical light transmitting slot cut out of saidcovering.

3. Means for scanning a picture field in suceessive elemental areas,comprising a first drum having scanning perforations therein arranged inthe peripheral wall thereof in the path of a plural turn helix, a secondtransparent drum having a non-transparent covering with a lighttransmitting slot extending around the periphery thereof, means forrotating both said drums simultaneously across the picture field, theperforations in the first drum and the slit in the second drum being soarranged with relation to the speeds of the respective drums that thepicture field is exposed to only one elemental area at a time.

t. A television scanning member comprising a transparent rotatablemember having a covering of nontransparent material thereon, and aspiral slot in said covering.

in testimony whereof I have hereunto set my hand.

CHARLES FRANCIS JENKINS.

